The present invention relates to mine roof support systems and, more specifically, to novel and improved mine roof supports employing truss systems with tensioned horizontal members.
The desireability of supporting mine roofs by means of horizontal members connected at their ends, and/or at intermediate points to anchoring members extending into drill holes formed for such purpose has long been recognized. Such systems are disclosed, for example, in 1925 U.S. Pat. No. 1,559,560 of Doughty and 1954 U.S. Pat. No. 2,667,037 of Thomas et al. It has further been recognized that added support capability is provided by additional tensioning of the horizontal member which connects the ends of the ends of the anchor members extending outside the holes, beyond the tension naturally resulting from installation of the anchor members at outwardly extending angles through the horizontal member. Such additional tensioning is shown, for example, in 1964 U.S. Pat. No. 3,163,012 of Dempsey, and 1969 and 1970 U.S. Pat. Nos. 3,427,811, 3,505,824, 3,504,726, all of White.
At the present state of commercial evolution of such truss systems, i.e., roof supports wherein a more or less horizontal member is tensioned between the lower ends of members anchored in upwardly extending drill holes, those presently in widest use, at least in this country, are used to supplement individually installed roof bolts. That is, as mining progresses into a seam, drill holes are formed in the roof at intervals prescribed by an approved roof support plan, and individual roof bolts are anchored within the hole and hold a bearing plate in contact with the area of the roof surrounding the openings. In a typical installation, for example, the roof bolts may be installed on four foot centers, resulting in a total of four bolts installed in a line laterally across a mine tunnel 20 feet in width.
In the present-day use of the truss systems referred to above, individual roof bolts are installed in the usual way as mining progresses to provide the necessary support in compliance with the approved roof plan. The truss system is usually installed at a later time, requiring the necessary machinery and personnel to be returned to the previously bolted area to install the truss system. The reason for this is the inordinately long time required to install the truss systems, unless additional machinery and personnel are employed, compared with the rate of advance of the mining operation. Even though sometimes justified by the increased safety provided by the added support capacity of the truss system, installation of such systems represents an enormous increase to the mining costs.
It is a principal object of the present invention to provide a truss system for mine roof support which can be installed as part of the regular mining cycle, i.e., an "in-cycle" truss system installation.
A further object is to provide a mine roof truss system wherein the anchoring members for the truss system provide part of the approved roof plan, replacing at least some of the individual anchor members in typical installations rather than being in addition thereto, thereby reducing the overall cost of the roof support system without any sacrifice in effectiveness.
Another object is to provide a mine roof support truss system having a greater range for tolerance of misalignment in both horizontal and vertical directions of the anchor members on each side of the truss without causing appreciable bending of the roof bolts, or causing appreciable movement of the roof plate used on the anchor members.
Still another object is to provide a truss system which may be tensioned more easily and at points removed from the center of the truss.
A still further object is to provide a truss system for mine roof support having a wide degree of latitude in the angles at which the drill holes for the anchor bolts may be formed.
Other objects will in part be obvious and will in part appear hereinafter.